Add backoff to reduce CPU usage (fixes #141) (#151)

* Add backoff to reduce CPU usage

* Update driver version for CPU fix

RaspberryPi/apple2driver/a2io/gpio.go

@@ -160,11 +160,18 @@ func (a2 A2Gpio) ReadByte() (byte, error) {
 
 	// wait for the Apple II to write
 	startTime := time.Now()
+	lastSleepTime := time.Now()
+	sleepDuration := 10
 	for inWrite.Read() == 1 {
 		if time.Since(startTime) > edgeTimeout {
 			outRead.High()
 			return 0, errors.New("timed out reading byte -- write stuck high")
 		}
+		if time.Since(lastSleepTime) > edgeTimeout/10 {
+			sleepDuration *= 3;
+			time.Sleep(time.Millisecond * time.Duration(sleepDuration));
+			lastSleepTime = time.Now()
+		}
 	}
 
 	// get a nibble of data
@@ -211,10 +218,17 @@ func (a2 A2Gpio) ReadByte() (byte, error) {
 	// wait for the Apple II to finish writing
 	//fmt.Printf("wait for the Apple II to finish writing\n")
 	startTime = time.Now()
+	lastSleepTime = time.Now()
+	sleepDuration = 10
 	for inWrite.Read() == 0 {
 		if time.Since(startTime) > edgeTimeout {
 			return 0, errors.New("timed out reading byte -- write stuck low")
 		}
+		if time.Since(lastSleepTime) > edgeTimeout/10 {
+			sleepDuration *= 3;
+			time.Sleep(time.Millisecond * time.Duration(sleepDuration));
+			lastSleepTime = time.Now()
+		}
 	}
 
 	return data, nil
@@ -230,11 +244,18 @@ func (a2 A2Gpio) WriteByte(data byte) error {
 
 	// wait for the Apple II to be ready to read
 	startTime := time.Now()
+	lastSleepTime := time.Now()
+	sleepDuration := 10
 	for inRead.Read() == 1 {
 		if time.Since(startTime) > edgeTimeout {
 			outWrite.High()
 			return errors.New("timed out writing byte -- read stuck high")
 		}
+		if time.Since(lastSleepTime) > edgeTimeout/10 {
+			sleepDuration *= 3;
+			time.Sleep(time.Millisecond * time.Duration(sleepDuration));
+			lastSleepTime = time.Now()
+		}
 	}
 
 	if ((data & 128) >> 7) == 1 {
@@ -291,11 +312,18 @@ func (a2 A2Gpio) WriteByte(data byte) error {
 	// wait for the Apple II to finsih reading
 	//fmt.Printf("wait for the Apple II to finsih reading\n")
 	startTime = time.Now()
+	lastSleepTime = time.Now()
+	sleepDuration = 10
 	for inRead.Read() == 0 {
 		if time.Since(startTime) > edgeTimeout {
 			outWrite.High()
 			return errors.New("timed out writing byte -- read stuck low")
 		}
+		if time.Since(lastSleepTime) > edgeTimeout/10 {
+			sleepDuration *= 3;
+			time.Sleep(time.Millisecond * time.Duration(sleepDuration));
+			lastSleepTime = time.Now()
+		}
 	}
 
 	// let the Apple II know we are done writing

RaspberryPi/apple2driver/driver.go

@@ -49,15 +49,12 @@ func main() {
 	handlers.SetCommunication(comm)
 	comm.Init()
 
-	lastCommandTime := time.Now()
-
 	// In case Apple II is waiting, send 0 byte to start
 	comm.WriteByte(0)
 
 	for {
 		command, err := comm.ReadByte()
 		if err == nil {
-			lastCommandTime = time.Now()
 			switch command {
 			case resetCommand:
 				handlers.ResetCommand()
@@ -77,7 +74,7 @@ func main() {
 				handlers.ShellCommand()
 			}
 			// temporary workaround for busy wait loop heating up the RPi
-		} else if time.Since(lastCommandTime) > time.Millisecond*100 {
+		} else {
 			time.Sleep(time.Millisecond * 100)
 		}
 	}

RaspberryPi/apple2driver/info/version.go

@@ -8,4 +8,4 @@ package info
 
 // Version is the hexadecimal version number that
 // should be incremented with each driver update
-const Version = "0029"
+const Version = "002A"